bendorf



United States Patent 3 124,714 VACUUM-TIGHT SEALS FGR KLYSTRON TUBES John R. Bendorf, Los Altos, Calif., assignor to Litton Precision Products, Inc., a corporation of Delaware Filed Aug. 18, 1961, Ser. No. 132,412 Claims. ($1. 315-539) This invention relates to improved vacuum-tight seals for high power electron tubes, and more particularly to improved vacuum-tight seals for high power multicavity klystron tubes wherein large cylindrical insulating ceramic sect-ions are sealed to correspondingly large size supporting metal sections.

In the construction of high power klystrons, the fabrication of joints between metal and ceramic parts in such a manner as to provide suflicient mechanical strength and to also provide an adequate vacuum seal has presented a considerable problem. A number of solutions to this problem have been proposed heretofore. In accordance with one known construction, particular sealing arrangements have been proposed for the ceramic and metal sections of a klystron tube envelope, especially those sections which are associated with the resonant cavities of the tube. In this construction, a plurality of resonators comprising a pair of copper end wall disks are connected by a cylindrical insulating ceramic wall section. The ceramic section is connected to the metal section by a sealing arrangement which consists of an outer cylindrical ring and an irregular shaped cylindrical ring having an inturned flange section. These two sections are brazed to each other along one end of their corresponding cylindrical walls; the other end of the outer cylindrical member being brazed to the end wall disk along its circumference, While the flange end :of the irregular shaped ring is brazed to one end of the ceramic wall. This prior art sealing arrangement is completed by a ceramic backing ring member aflixed to the inturned flange end of the inner ring member to provide a nonmetallic support surface for a sliding joint with the end wall disk member. Each resonant cavity has one of the sealing arrangements at each end of the cylindrical ceramic member to form a vacuum-tight envelope.

While the prior device is adequate for some purposes, in practice it has been found that there are several distinct disadvantages attendant its use. These disadvantages stem primarily from the inherent properties of the brazed joint, that is, the differences in coefiicient expansion of the materials used and shear forces acting on the joint.

More particularly, the ceramic backing ring is generally of a harder material than the abutting end disk, which is usually copper. As the tube heats up and cools oif, the ceramic bites into the copper after a number of cycles. As this process progresses, the sharp edges of the ceramic adjacent the end disk may gall at both the outer and inner edges of the ceramic. In any event, when the ceramic galls at either edge it is subject to a shear force at the edges. The edges of the ceramic in contact with the metal surface may be chipped away and a shear force or bending moment, or both, is exerted on the seal between the ceramic backing ring and main body of the ceramic cylinder. Since it is well known that the ceramic-to-metal seal is weaker in shear than in tension or compression, it experiences a high rupture rate when the tubes in which it is employed are being handled. This arises because of the unusually large size of the tubes in which these seals are used. Thus, it has been found that an initial crack or slight rupture may occur between the main ceramic member and the inner metal ring member, which ultimately results in a break in seal causing the tube to lose its vacuum by air leaking through the seal.

As noted above, the need for strong vacuum-tight seals is extremely important in klystron tubes of large physical Patented Mar. it), 1964 size. Presently, one of the largest varieties in production is one nine feet in length and as much as eight hundredfifty pounds in weight. The size of these tubes make them more vulnerable to slight cracks part way through the ceramic or ceramic-tdmetal seals, which might be tolerated in a small tube. Such slight cracks are fatal to the larger tubes, because of their large size the crack is aggravated when the tube is handled and the crack extends completely through the ceramic or the seal.

The ceramic insulators are also necessary in these large size klystrons because it may be desirable to exhaust the tubes at a significantly higher temperature than prior art tubes which utilized glass as the insulator material. In the priort art, the tubes which employed glass were incapable of being exhausted above a temperature of about 500 C. without causing the glass to lose its physical strength and to be pushed in by the differential betwee. atmospheric pressure and the vacuum within the tube. Commercially available ceramic materials, on the other hand, are capable of being heated to temperatures in excess of 1600 C. with no loss in physical strength. Thus, the differential between the atmospheric pressure and the vacuum inside the tube does not cause the ceramic to rupture thereby losing the vacuum in the tube.

The present invention obviates the foregoing and other distadvantages of the prior art seals by providing a vacuum-tight sealing arrangement wherein the vacuum-tight seal is no longer subjected to rupturing forces which tend to weaken or crack the seals. In accordance with an illustrative embodiment of the present invention, there is provided a rugged vacuum-tight seal arrangement having the ceramic-t-o-metal vacuum seals under tension or compression forces. The forces exerted on the ceramic-tometal seal are shared axially by the main ceramic section in the form of support. The end support member which may be made of a suitable material such as copper or stainless steel in this embodiment, is supported in sliding abutment relationship at both ends of the cylindrical wall to provide significant stress relief for the associated vacuum seals.

Another embodiment of the invention provides a flat ridge surface on the bearing surface of the support members. The diameter of the ridge corresponds generally to the diameter of the associated main ceramic section, having a width slightly less than the thickness of the ceramic cylinder. The ridges upon which the ceramic sections abut tend to prevent the edges of the ceramic from cutting into the support members thereby avoiding gall-ing and chipping difliculties encountered in the prior art sealing arrangements employing the ceramic backing rings. As the ceramic slides back and forth on the ridged surface, it may become cold worked so that its resistance to wear increases with the life of the tube. In any event, the ridges are raised sufiiciently enough initially to insure that the ceramic will never rest directly on the end support member during the life of the tube.

The ceramic-to-metal seal may be of any suitable type known in the prior art. The ceramic-to-metal seal disclosed United States patent Serial Number 2,972,808, granted February 28, 1961, by Charles V. Litton, entitled Ceramic-to-Metal Seals, has been used satisfactorily in the practice of this invention. As described in the Litton patent, the cylindrical ceramic and vmetal sleeve are tapered in a conjugate manner over a relatively large seal region to provide added structural strength, such as that required for the large size ceramic section under consideration.

It is, therefore, an object of the invention to provide a physically strong vacuum-tight seal for unusually large electron discharge devices requiring ceramic-to-metal seals.

Another object of the invention is to provide an improved flexible vacuumstight ceramic-to-metal seal ar- 3 rangement having extra large size cylindrical ceramic sections.

A further object of the invention is to provide a ceramic support arrangement wherein the ends of the cylindrical ceramic insulator wall carries a large portion of the compression forces which are developed in the vacuum seal arrangement.

Still another object of the invention is to provide a vacuum-tight seal arrangement which will be free of undesirable shearing forces which maycrack the seal'and result in loss of vacuum in the tube.

Yet another object of the invention is to'provide a vacuum-tight seal in which the metal members of the seal arrangement will yield under tensile or compression forces without rupturing the ceramic-to-metal seal.

The novelfeatures which are believed to be characteristic of the invention both as to its organization and method of construction, together with further objects and advantages thereof, will be better understood from the following description considered in connection with the accompanying drawings in which several embodiments of the invention are illustrated by way of example. It is to be expressly understood, however, that the drawings are for the purpose of illustration and description only and are not intended as a definition of the limits of either the articles or methods of construction of the invention.

FIGURE 1 is a diagrammatic View, partly in crosssection, of a klystron amplifier tube illustrating the manner in which the ceramic-to-metal seal arrangement may be employed to provide electrical insulation between high voltage electrodes of the tube in accordance with the invention;

FIGURE 2 is a fragmentary view of the klystron'tube shown in FIGURE 1, illustrating the details of the ceramic-to-metal seal arrangement in accordance with the present invention;

FIGURE 3 is a fragmentary View of the klystron tube shown in FIGURE 1, illustrating the details of alternative configuration for the vacuum seal arrangement of the invention; and

FIGURE 4 is a fragmentary view of the klystron tube shown in FIGURE 1 illustrating the details of another alternative configuration forthe vacuum seal arrangement of the invention.

With reference now to the drawings, wherein like or corresponding parts are designated by the same reference characters throughout the several views, there is shown in FIGURE 1 a high power klystron amplifier tube 10. As shown in FIGURE 1, klystron comprises, basically, an electron gun section generally designated 12 having a cathode 14 for producing an electron beam, and a cathode connection 15 which is used to provide a current potential to cathode 14. A beam control-and focusing electrode for forming an electron beam and controlling the flow of electrons encloses the region about the cathode. A first anode and'drift tube 18 is in axial alignment with the control electrode 16 and a second drift tube N which is one of several drift tubes of the device. The other drift tubes have not been shown in the interest of making the description brief.

Within'a first cavity resonator 2 2, which is formed by a cylindrical enclosure member 24, a first end plate and anode terminal 26 connected concentrically to the first drift tube 18, and a second end plate 28 connected concentrically to the second drift tube 20. The cavity 22 also includes an input terminal 30 for coupling an input signal into the cavity to be amplified and a tuner device 32 for tuning the resonance frequency of the cavity 22.

Continuing with the brief description of FIGURE l, the klystron has a large collector electrode 34 disposed at the remote end of the tube along the path of the electron beam and axis of the tube for collecting the electrons of the beam. The collector may have a fluid cooling apparatus associated therewith, which has not been shown in detail. A pair of tubular openings and connections 36 and 38 are utilized respectively as the inlet and outlet openings for the cooling apparatus. The tube is completed by an output transmission line 40 for coupling power from the tube to an associated external load.

Consider now, with greater particularity, the vacuumtight seal arrangement shown in FIGURE '1 designated by the area encompassed by a dashed-line circle 42, and shown in FIGURE 2 in an enlarged view. As shown in FIGURE 1 of the drawing, the cathode connection 15 is electrically isolated from the control electrode 16 by a first ceramic insulator section 44 while controlelectrode 16is electrically isolated from the first drift tube 18 by a second ceramic insulator section 46 The need for these ceramic sections arises from the fact that the voltages between the-electrodesis-unusually high. For example, in the present embodiment the cathode connection 15 may be biased at a negative one hundred-twenty kilovolts withrespect to ground. Thefirst drift tube 18 is-at ground potential, while the control electrode 16 swings between negative one hundred-twenty kilovolts and negative fifty-five kilovolts.

Under such high voltage'conditions, it is desirable to have aninsulation'materi'al such as ceramic'which'wilh withstand extreme temperature effects of a high voltage electron beam. In addition, the size of the tube further increases the need for large size insulator cylinders to withstand the pressure differential between the outside atmosphere and the vacuum within the tube which is addition to the ceramic cylinder 44 and the flange 48 of the cathode connection 15 which are to be-vacuously connected. The terms vacuously connected or vacuously sealed as used in the present specification and claims, signifies connected in a vacuum-tight manner or the making'of a vacuum-tight connection.

One element is a first sleeve or cylindrical ring member 52, one end of which has been tapered to mate conjugately with a tapered surface 54 of the ceramic cylinder 44; theother end of ring 52 has a-flange end 56. The other vacuum sealing element is a second sleeve or cylindrical ring member 58 which has one end flared outwardly. It should be noted at this point, that ring members 52 and 58 aremadeof relatively thin materials;

ticular ceramic material employed in forming ceramiccylinder 44. The two members 44- and 52-rnay be vacuously connected along tapered surface 54 of ceramic 44 in-a manner similar to that described in the aforementionedLitton patent forceramic-to-metal seals.- The second cylindrical ringmember 58 may also be constructed of kovar and is connected, as by brazing, atone end to support flange 48along-surface libetween flange 48 and cylindrical ring 58 forming-a vacuum-tight seal; Although'cylinder ring 58 maybe made ofkovar, it is preferablymade of a nonmagnetic material whose coefiicient of expansion is close to that of flange 48. The other endof ring 58 and ring member 52 are sealed'toadjoining edge designated 62.

As shown in FIGURE 2, support flange 48 has a ridge.

64 whose median diameter is about that of the ceramic cylinder 44 and has a width slightly less than that of the ends of cylinder 44 designated 66. The cylinder 44 abuts against flange 48 and removes a substantial portion of the axial forces acting on the seal connections between ring member 52 and the ceramic cylinder 44 and the ring member 58 and flange 4-8. Thus, these seals are stress relieved by the abutting arrangement between the ceramic cylinder and flange 48. More particularly, the vacuous seals at surfaces 54 and 60, and edge 62 are stress free in their normal position as shown in FIGURE 2. These seals are subjected to slight stresses when the ceramic cylinder 44 is not in absolute axis alignment due to distortions caused by handling of the tube or different coefficients of expansion between the various elements during exhaust at high temperatures.

Referring now to FIGURE 3, there is shown an alternative configuration for the vacuum seal arrangement illustrating a double seal. The arrangement shown in FIGURE 3, within the dashed-line circle 68, is similar to the single seal 50 in that it has two seals like seal 50 which may be considered disposed back-to-back. As shown, the tapered surfaces of cylinders 44 and 46 are each respectively cormected to one end of a ring member 52 in the same manner as those shown in FIGURE 2. The other end of each ring 52 is connected to opposite ends of a common U-shaped ring or a symmetrical double flanged member '70. The middle section of the U-shaped member '70 is connected to a concentric support flange section 72 of focusing electrode 16 along a surface 74. The connection along surface 74 is within the vacuum enclosure formed by ceramic cylinders 44 and 46 with rings 52, and ring '70 with rings 52. Thus, the connection along surface 74 is not essential as a vacuum seal, but is utilized as a support connection. Two semicircular rings 76 are connected to the outer surface U-shaped ring member 70 as reinforcement to hold member '70 in place and to provide a heat conduction path from the drift tube section of electrode 16 for transferring heat generated therein by electrons of the beam impinging upon the electrode. Ring '76 also provides an electrical contact point for a corona shield, which has not been shown, that may be employed to eliminate electrical break-downs in the region surrounding the seals. The U-shaped ring member 70 is preferably made of a material having a coeflicient of expansion close to that of flange member '72 so that buckling of ring 70 is avoided.

FIGURE 4 shows another illustrative alternative configuration for the seal arrangement according to the in- V vention. As shown within the dashed-line circle 78, the

seal arrangement has been designated 50 including a tapered conjugated seal between ceramic cylinder 46 and ring 52, and a vacuum-tight seal between a thin cup-like ring element 80 having a flange 82 and ring 52.

Cup-like element 30 has a ridge 64 abutting in spaced relationship with end 66 of support cylinder 46. The cup like element 80 is connected to a support flange 84 which forms a portion of the first drift tube and anode connection 13.

Cup-like member 80 may be made of any suitable nonmagnetic material, such as stainless steel, whose coeflicent of expansion is close to that of flange 84. The flange ends of ring element 52 and cup-like element 80 are connected together in a vacuum-tight seal along a common edge 86, as by welding for example. In a similar manner, as shown in FIGURES 2 and 3, the seal shown in FIGURE 4 designated 50 is stress relieved by the fact that the end 66 of the ceramic cylinder 46 provides substantially complete axial support in the arrangement.

Consider now the advantages which are provided by the vacuum-tight sealing arrangement of the invention. Owing to the high physical strength of the annular ring members 58, 70 and 80, which may be made of nonmagnetic materials such as stainless steel for example,

and kovar ring member 52, and that of the insulating ceramic support cylinders 44 and 46, it is possible to provide a vacuum-tight arrangement that is substantially unaffected by the relatively high temperatures encountered in exhausting the klystron tubes. The ability of the ceramic to withstand temperature, while maintaining its physical strength, is especially significant since it is desirable to exhaust the tubes at unusually high temperatures such as 600 C. to 700 C. for example. In addition, the physical strength of these elements at ambient temperatures makes the sealing arrangement rugged and less susceptible to cracks and ruptures clue to handling of the tube during shipment or installation in equipment for operation.

Another advantage of the invention is derived from the use of relatively thin flexible annular ring members in conjunction with the stress relieving function of the ceramic cylinders. These flexible annular rings are mechanically strong and enable the disclosed seal arrangement to withstand large bending forces without permanent deformation while providing significant stress relief for the vacuum-tight joints of the arrangements. A major portion of the stress relief in the present arrangement is provided by the ceramic insulating cylinders, inasmuch as the ends of these cylinders are in abutting relationship with the bearing surfaces of the ridges formed on the support members. Finally, the provision of the ridge surfaces on the support members significantly reduce the frictional forces between the end of the ceramic cylinder and support member and permits free sliding movement therebetween. Thus, the sliding joint arrangement eliminates the undesirable gailing, chipping or cracking of the end ceramic cylinder. Furthermore, there is no ceramicto-metal seal as part of the sliding joint thereby eliminating one of the major factors causing shearing failures of the seal arrangement of the prior art discussed hereinabove.

In practice it has been found that a high grade ceramic, such as the AL 300 ceramic, 97.6 percent aluminum oxide (A1 0 available from the Western Gold and Platinum Company of 525 Harbor Boulevard, Belmont, California, about eight inches hi h, nine to ten inches in diameter and three-quarters of an inch thick may be used as the ceramic cylinder i l and 46. This ceramic material is capable of withstanding temperatures as high as 1600 C. and compression forces in excess of 200,000 pounds per square inch without any deformation or deterioration. These unusually large size ceramic cylinders may be used in the illustrative embodiment of the invention in the unusually large size klystron tubes which are in greater demand for military applications. Thus, these klystron tubes may be exhausted at a temperature in excess of 600 C. providing unusually good vacuums, about 10* mm. Hg, insuring greater reliability and longer life for such tubes.

While the vacuum-tight seal arrangement of the invention has been described with reference to several particular embodiments, it will be understood that various modifications could be made in the construction and arrangement thereof without departing from the spirit and scope of the invention. Thus, by way of example but not of limitation, the cylindrical ring element, for example ring 58, which is connected to the support flange 48 may be replaced by a flexible element as part of flange 48 which is welded directly to a modified version of ring element 52. Accordingly, it is to be expressly understood that the foregoing description shall be interpreted only as illustrative of the invention, and that the appended claims be accorded as broad an interpretation as is consistent with the basic concept herein taught.

What is claimed as new is:

1. In a klystron amplifier tube of the velocity modulation type for amplifying an input signal having a plurality of ceramic-to-metal seals forming a vacuum-tight envelope, said tube comprising: means for producing a a beam of electrons along a predetermined axis of said tube, said means including a first circular suport flange; means for controlling the flow of electrons of said beam, said means including a second cylindrical support flange; drift tube means surrounding the path of said electron beam, said drift tube means including a third support flange; an electrode for collecting the electrons in said beam; an output means for extracting an amplified signal from said tube; said ceramic-to-metal seals including a first ceramic cylinder having one end in sliding abutment with said first support flange and a first composite seal member including a pair of flexible cylindrical ring members having one end making a vacuum-tight connection with said first ceramic cylinder and the other end making a vacuum-tight connection with said first support flange, the other end of said first ceramic cylinder in sliding abutment with one side of said second support flange and one end of a second ceramic cylinder in sliding abutment on the other side of said second support flange opposite said first ceramic cylinder, said first and second ceramic cylinders being connected in a vacuum-tight manner to a second composite ring member including a pair of circular ring members each making a vacuum-tight connection at opposite ends of a U-shaped cylindrical member, said U-shapcd cylindrical member being connected to said second support flange member, the other end of said second ceramic cylinder in sliding abutment with said third support flange and a third composite member including a pair of flexible cylindrical ring members connected in a vacuum-tight manner having one end making a vacuum-tight connection with the other end of said second ceramic cylinder and the other end of the ring making a vacuum-tight connection with said third support flange to complete the vacuum envelope of said tube.

2. An improved vacuum-tight seal arrangement for electron discharge tubes having a main body comprising: a ceramic cylinder section having at each end thereof a tapered surface section; a first flexible metallic cylindrical rin ghaving at one end thereof a tapered surface corresponding to said tapered surface section of said ceramic cylinder and being connected in a vacuum-tight manner and uniformly engaging a portion of said tapered surface of said ceramic cylinder, said first ring member having an outward flared flange at the other end; a support flange forming part of the body of said tube having a raised ridge, said ridge having a surface in abutting relationship with one end of the ceramic cylinder and in symmetrical alignment with said ceramic cylinder, said ridge having a width less than the thickness of said end of said ceramic cylinder and a median diameter equal to said ceramic cylinder; a second flexible metallic cylindrical ring making a vacuum-tight connection at one end to the flange of said first ring and making a vacuumtight connection at the other end to the cylindrical surface edge of said cylindrical support flange completing said vacuum-tight seal arrangement.

3 An improved vacuum-tight seal arrangement for an electron discharge tube comprising: a pair of ceramic cylinder sections each having a tapered surface section at both ends; a pair of flexible metallic cylindrical single flange ring members each having at one end a tapered surface complementary to said tapered surface of said ceramic cylinder and being vacuously sealed to and uniformly engaging a portion of the tapered surface of said ceramic cylinder, the other end of said ring forming a flange; and a U-shaped ring member having two outward flared flange ends, each connected to the flange ends of said single flange ring member forming a pair of vacuumtight seals and being connected at its cylindrical middle section to a cylindrical support flange forming a part of the electron discharge tube.

4. An improved vacuum-tight seal arrangement for an electron discharge tube having a main body, said seal arrangement comprising a ceramic cylinder section having a given transverse dimension and having at each end thereof a tapered surface section, a flexible metallic cylindrical ring having a tapered surface at one end corresponding to the taper of said ceramic cylinder, and being vacuously sealed to and uniformly engaging a portion of the tapered surface of said ceramic cylinder, a flexible metallic circular cup like member including an outward flared flange end and a depressed flat cup surface, said depressed surface having a raised ridge, said ridge having a surface having a transverse dimension less than that of the given transverse dimension of said ceramic cylinder and a width less than the thickness .of the end of the ceramic section adjacent thereto, the end of said ceramic cylinder being in abutting relationship and in symmetrical alignment with said ridge, the other end of said flexible metallic cylindrical ring being vacuously sealed to said flange end of said cup-like member, the flat surface of said depressed cup on the other side of said ridge being vacuously sealed to a flange forming part of the main body of said tube to complete the vacuum-tight seal arrangement.

5. A vacuum-tight enclosure comprising first and second ceramic tubular sections disposed end-to-end with adjacent ends in sliding abutment on opposite sides of a support flange therebetween, said adjacent ends of said ceramic sections and support flange being vacuously connected to a first flexible metallic sealing structure, the remote ends of said first ceramic sections being in sliding abutment with a second support flange member and vacuously connected thereto by a second flexible metallic annular sea-ling structure, the other end of said second ceramic section being in sliding abutment with a cuplike member vacuously connected to a third support flange, said second ceramic section being vacuously connected to said cup-like member and said ceramic section to complete the va'cuumt-ight enclosure.

6. An improved vacuum-tight seal comprising: a circular cathode connector flange member having an inner concentric raised ridge surface and an outer cylindrical flange surface extending radially; a ceramic cylinder having one end in axial alignment and symmetrically sliding abutment with said ridge; and a pair of cylindrical ring members each having an outwardly extending flange end and being connected to one another along said flange ends in a vacuum seal forming a composite member, one end of said composite member being connected to said ceramic cylinder in a vacuum-tight seal and the other end being connected to said cathod connector flange member in a vacuum-tight seal along said axially extending cylindrical flange surface to complete the vacuum seal.

7. An improved vacuum-(tight seal comprising: a cirucular cathode connector flange member having an inner concentric raised ridge surface and an outer cylindrical flange surface extending radially; an insulator cylinder having one end in axial alignment and a symmetrically sliding abutment with said ridge, said insulator cylinder having a tapered surface section near the abutting end thereof; a pair of cylindrical ring members each having an outwardly extending flange end and being connected to one another along said flange ends; and a vacuumiight seal forming a composite member, one end of said composite member having a tapered suriace corresponding to that of said insulator cylinder making a vacuum-tight seal with said insulator cylinder and the outer end making a vacuum-tight seal with said cathode connector flange member along said axially extending cylindrical flange surface to complete the vacuum seal.

8. An improved vacuum-tight seal comprising: a pair of ceramic cylinders disposed in sequential alignment in abutting spaced relationship on opposite sides of a supporting flange common to and separating said cylinders; a pair of cylindrical first vacuum-seal ring members each having an outwardly extending flange at one end and a tapered surface at the other end which corresponds to the surface of the ceramic cylinders; and a U-sliaped vacuum seal ring member having a depressed flat surface, said member being connected to the flange ends of each of said first ring members forming a composite ring memher, said composite ring member being vacuously sealed to said ceramic cylinders and said supporting flange to complete the vacuum-tight seal.

9. An improved vacuum-tight seal arrangement for an electron discharge tube having a main body, said seal agrangernent comprising: an insulator cylinder section having a tapered surface section at each end; a metallic cylindrical ring member having a tapered surface at one end corresponding to the taper of said insulator cylinder and being vacuously sealed to and uniformly engaging a portion of the tapered surface of said insulator cylinder, said ring member having an outwardly extending flange at the other end; a cupular member having an outwardly extending flange and a flat depressed surface having a concentric raised ilat ridge, said ridge having a surface having a median circumference equal to that oi the insulator cylinder, the end of said insulator cylinder being in sliding abutment with said ridge surface, the other end of said metallic ring member being vacuously sealed to the flange end of said cupular member and the flat depressed su-rfiace of said cupular member being vacuously sealed to a flange forming part of the main body of said tube to complete the vacuum-tight seal arrangement.

10. An improved vacuum-tight seal arrangement for electron dicharge tubes having a main body comprising: a ceramic cylinder section havhrg at each end thereof a tapered surface section; a first flexible metallic cylindrical ring having at one end thereof a tapered surface corresponding to said tapered surface section of said ceramic cylinder and being vacuonsly sealed to a portion of said tapered surface of said ceramic cylinder, said first ring member having an outward flared fllange at the other end; a support flange forming part of the body of said tube having a raised ridge, said ridge having a surface in abutting relationship with one end or the ceramic cylinder and in symmetrical alignment with said ceramic cylinder, said ridge having a Width less than the thickness of said end of said ceramic cylinder and a median diameter equal to said ceramic cylinder; a second flexible metallic cylindrical ring being yacuously sealed at one end tothe flange of said first ring and vacuously sealed at the other end to the cylindrical surface edge of said cylindrical support flange completing said vacuum-(tight seal arrangement.

References Cited in the file of this patent UNITED STATES PATENTS 2,812,466 Murdock Nov. 5, 1957 2,879,428 Williams Mar. 24, 1959 2,993,614 Preist Sept. 8, 1959 

3. AN IMPROVED VACUUM-TIGHT SEAL ARRANGEMENT FOR AN ELECTRON DISCHARGE TUBE COMPRISING: A PAIR OF CERAMIC CYLINDER SECTIONS EACH HAVING A TAPERED SURFACE SECTION AT BOTH ENDS; A PAIR OF FLEXIBLE METALLIC CYLINDRICAL SINGLE FLANGE RING MEMBERS EACH HAVING AT ONE END A TAPERED SURFACE COMPLEMENTARY TO SAID TAPERED SURFACE OF SAID CERAMIC CYLINDER AND BEING VACUOUSLY SEALED TO AND UNIFORMLY ENGAGING A PORTION OF THE TAPERED SURFACE OF SAID CERAMIC CYLINDER, THE OTHER END OF SAID RING FORMING A FLANGE; AND A U-SHAPED RING MEMBER HAVING TWO OUTWARD FLARED FLANGE ENDS, EACH CONNECTED TO THE FLANGE ENDS OF SAID SINGLE FLANGE RING MEMBER FORMING A PAIR OF VACUUMTIGHT SEALS AND BEING CONNECTED AT ITS CYLINDRICAL MIDDLE 